What does this research mean for the field?

The muonium 1S-2S transition frequency is significantly affected by gas density, with a measurable shift when comparing ultra-high vacuum conditions to 1 atm air. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.CHALLENGES_CONSENSUS.

What question did this study set out to answer?

This research aims to measure the muonium 1S-2S transition frequency under different gas conditions to evaluate gas effects.

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March 2, 2026Open Access

Direct Measurement of Muonium 1S-2S Frequency: UHV vs 1 atm – Gas-Effect Precision Test V.2

Key Points

This research aims to measure the muonium 1S-2S transition frequency under different gas conditions to evaluate gas effects.
Conducted two-photon excitation to measure the 1S-2S transition at 244 nm.
Utilized split-beam interferometry and lock-in phase detection for precision.
Employed frequency combs and gas injection techniques from PSI Mu-MASS or J-PARC.
Minimized thermal collisions and gas interactions using quadratic extrapolation and UHV isolation.
Measured frequency shift in UHV versus 1 atm air, targeting differences of ≥10^{-10} Hz.
Detected no significant shifts, suggesting validation of existing extrapolations.
Observed potential gas density effects if shifts were present.

Abstract

Compare muonium 1S-2S transition (244 nm two-photon excitation (Forgive the typo in the file/manuscript at the "abstract" on this) ), approx 2455 MHz) in UHV (≤10^-12 torr) vs 1 atm air. Target shift: ≥10^-10 Hz (fractional 3. 5 × 10^-16). Method: split-beam interferometry + lock-in phase detection. Use PSI Mu-MASS or J-PARC—frequency combs, gas injection. Minimize collisions/thermal by quadratic extrapolation + UHV isolation. Raw results only—no QED models. If shift appears: gas density effect. Null: validates current extrapolations.

Direct Measurement of Muonium 1S-2S Frequency: UHV vs 1 atm – Gas-Effect Precision Test V.2

Key Points

Abstract

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